This invention relates to a process for electrolytically producing a low silica metallic oxide as a raw material of Mn-Zn ferrite, Mg ferrite, Fe-Zn ferrite to be or Fe-Ni ferrite used for various types of magnetic materials.
Oxide ferrites are widely used industrially as magnetic materials. The chemical composition of the oxide ferrite includes MO.M'.sub.2 O.sub.3, where M generally signifies a two-valency metal such as, for example, iron, manganese, zinc, magnesium, nickel, cobalt, copper, lead, cadmium, barium, or strontium, and M' signifies a three-valency metal usually iron. The oxides of these metals are coupled by in a one to one molar ratio (e.g., in the ferrite oxide one moleof two-valency metallic oxide (MO) and one mole of three-valency metallic oxide (M'.sub.2 O.sub.3) are coupled in a 1:1 molar ratio), and normally called "a spinel type structure".
When the oxide ferrite is industrially produced, the metal oxide is finely pulverized, adequate amounts are mixed, molded, and calcined. It is well known that the purity of the metal oxide of raw materials for the ferrite largely affects the magnetic performance of the ferrite. Particularly, since silica in the raw material for the ferrite deteriorates the performance of the ferrite, a low silica magnetic material is needed but cannot be produced according to conventional processes. Various processes for producing the low silica metal oxides have been proposed.
For instance, an iron sulfate process which presently is most widely adopted for the treatment of an iron oxide, recrystallizes an iron sulfate and refines the recrystalized iron sulfate. However, ferrous sulfate crystallized by this process unavoidably includes a mother liquor. The ferrous sulfate must be washed with water to remove the mother liquor. Furthermore, the recrystallization must be repeated several times since the crystallized ferrous sulfate is melted, by washing with water. This results in an extremely inefficient and uneconomical process.
Another known process for isolating and removing silicon oxide SiO.sub.2 from a raw material solution includes oxidizing or treating the solution with a sulfuric acid solution while heating under pressure, washing with water, separating and removing the silicon oxide by adding a high molecular weight flocculant to the solution to flocculate the silicon oxide, and then filtering and separating the silicon oxide. A process for separating and removing silicon oxide from an iron chloride solution by partially extracting the silicon oxide by a solvent extraction process and distilling it is also known.
The above-described processes all necessitate the use of particular additives such as the high molecular weight flocculant or the extracting solvent to separate and remove the silicon oxide. These processes also require special equipment such as a pressurizing device. These processes, therefore, have drawbacks such as complicated process steps and high cost. In addition, according to these processes, the silicon oxide content can be reduced to approx. 70 ppm, but it is difficult to reduce the silicon oxide content to 70 ppm or lower.
Consequently, in order to produce ferrite with a content of silicon oxide of 70 ppm or lower previously electrolytic iron had to be dissolved in nitric acid to form iron nitride or to produce ferrite with a silicon oxide content of 30 to 50 ppm ferric oxide by it was necessary to thermally decompose high purity iron oxalate using ferric oxide. These processes are very expensive.
It is also known to produce low silica ferrite (e.g., Mn.sub.0.5 Zn.sub.0.5 Fe.sub.2 O.sub.4; Ni.sub.0.5 Zn.sub.0.5 Fe.sub.2 O.sub.4, etc.), by mixing oxide powders of low silica manganese, zinc, magnesium, nickel, barium or strontium with low silica ferric oxide, molding the mixture and calcining.
However, even when metal oxides such as manganese or zinc are mixed with iron oxide or iron manganese composite oxide, the grain size of the metal oxide is irregular, the mixture cannot be uniformly mixed mechanically, and when the mixture is calcined into a ferrite, the ferrite is irregular in its performance.